Near-field light generating method, near-field exposure mask, and near-field exposure method and apparatus

ABSTRACT

A near-field light generating method for forming a fine light spot at a portion adjacent to a fine opening having a size of not more than a wavelength of light on a light outgoing side of the fine opening by irradiating the fine opening with the light includes a step of forming a light spot having a length and a width which are substantially equal to each other by the fine opening. The fine opening has a rectangular shape having a length and a width which are different from each other.

TECHNICAL FIELD

The present invention relates to a near-field light generating method, anear-field exposure mask, a near-field exposure method, a near-fieldexposure apparatus, a near-field optical head, a near-field opticalmicroscope, and a recording and reproducing an apparatus.

PRIOR ART

Increasing capacity of a semiconductor memory and increasing speed anddensity of a CPU processor have inevitably necessitated furtherimprovements in fineness of microprocessing through optical lithography.Generally, the limit of microprocessing with an optical lithographicapparatus is of an order of the wavelength of light used. Thus, thewavelength of light used in optical lithographic apparatuses has beenshortened more and more. Currently, near ultraviolet laser is used, andmicroprocessing of 0.1 μm order is enabled. While the fineness is beingimproved in the optical lithography, in order to assure microprocessingof 0.1 μm or narrower, there still remain many unsolved problems such asfurther shortening of wavelength of laser light, development of lensesusable in such wavelength region, and the like.

On the other hand, as a means for enabling microprocessing of 0.1 μm ornarrower, a microprocessing apparatus using a principle of a near-fieldoptical microscope (scanning near-field optical microscope: SNOM), hasbeen proposed. For example, an exposure method in which, by use ofnear-field light leaking from a fine slit of a size not greater than 100nm, local exposure that exceeds the light wavelength limit is performedto a resist, has been proposed.

As means for such a purpose, a method of performing microprocessings inwhich a near-field probe is provided and a near field is generated bylocalized plasmon generated in a metal pattern to effectmicroprocessing. In this method, however, microprocessing is performedwith one or more processing probes, as like unicursal drawing so thatthroughput is not necessarily improved satisfactory.

As another method, Japanese Laid-OPen Patent Application (JP-A) No. Hei08-179493 has proposed such a method that a photomask with a fineopening pattern having a size of not more than a wavelength of light isprovided with a prism, the light is caused to enter the photomask at anangle causing total reflection, and a pattern of the photomask issimultaneously transferred to a resist by use of evanescent lightleaking from the total reflection surface.

Further, U.S. Pat. No. 6,171,730 has disclosed such an exposuretechnique that a photomask including a light blocking film having anopening pattern of not more than 0.1 μm is irradiated with light fromits back side and by use of near-field light leaking from the openingpattern, the pattern of the photomask is simultaneously transferred to aresist.

However, with respect to the above described methods in which thenear-field light is generated by use of the photomask having a fineopening pattern, a further improvement in generation efficiency ofnear-field light and generation of higher intensity near-field light aredesired.

DISCLOSURE OF THE INVENTION

An object of the present invention is to provide a near-field lightgenerating method and a near-field exposure mask which permit ahigher-efficiency generation of intenser near-field light.

Another object of the present invention is to provide near-fieldexposure method and apparatus and a near-field light optical head whichutilizes the above method or the mask.

A further object of the present invention is to provide a near-fieldoptical microscope and a recording and reproducing apparatus which usethe near-field optical head.

According to the present invention, there is provided a near-field lightgenerating method for forming a fine light spot at a portion adjacent toa fine opening having a size of not more than a wavelength of light on alight outgoing side of the fine opening by irradiating the fine openingwith the light, the method comprising:

forming a light spot having a length and a width which are substantiallyequal to each other by the fine opening, the fine opening having arectangular shape having a length and a width which are different fromeach other.

In the above near-field light generating method, the length and thewidth of the light spot may be determined by the width of therectangular opening.

In the near-field generating method, the fine opening may be provided ina plurality of fine openings including the rectangular opening and aslit-like opening.

According to the present invention, there is also provided a near-fieldexposure mask, comprising:

a mask base material,

a light blocking layer disposed on the mask base material, and

a fine opening having a size of not more than a wavelength of light usedfor exposure,

wherein the fine opening comprises a rectangular opening having a lengthand a width which are different from each other, the rectangular openinghaving a length/width ratio which permits transfer of a pattern having alength and a width which are substantially equal to each other.

In the near-field exposure mask, the fine opening is provided in aplurality of fine openings including the rectangular opening and aslit-like opening. Further, the fine opening has a length/width ratio of1.1-2.

According to the present invention, there is further provided anear-field exposure method, comprising: providing the near-fieldexposure mask described above, and exposure an exposure object to lightby using the A near-field exposure mask.

According to the present invention, there is further provided anear-field exposure apparatus for exposing an exposure object to light,comprising: the near-field exposure mask described above, and a lightsource to be exposed to light.

According to the present invention, there is further provided anear-field optical head, comprising:

means for generating near-field light, provided with a rectangular fineopening having a size of not more than a wavelength of light or acombination of the rectangular fine opening and a slit-like opening,

wherein a light spot having a length and a width which are substantiallyequal to each other by the rectangular fine opening, is formed at aportion adjacent to an opening portion on a light outgoing side of therectangular fine opening.

According to the present invention, there is further provided anear-field optical microscope for effecting surface observation of asample, comprising: a near-field optical head described above.

According to the present invention, there is further provided arecording and reproducing apparatus for effecting recording andreproduction with respect to a recording medium, comprising: thenear-field optical head described above.

These and other objects, features and advantages of the presentinvention will become more apparent upon a consideration of thefollowing description of the preferred embodiments of the presentinvention taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view showing a structure of a near-field exposurephotomask according to an Embodiment of the present invention.

FIGS. 2(a) and 2(b) are schematic views showing analysis results ofnear-field light by the near-field exposure photomask, wherein FIG. 2(a)shows a near-field distribution in the neighborhood of a rectangularopening in the Embodiment of the present invention and FIG. 2(b) shows anear-field distribution in the neighborhood of a square opening as acomparative Embodiment.

FIG. 3 is a schematic view showing a structure of a near-field exposureapparatus in Embodiment 1 of the present invention.

FIGS. 4(a) to 4(d) are schematic views for illustrating a method ofmanufacturing a near-field exposure photomask in Embodiment 1 of thepresent invention.

FIGS. 5(a) to 5(d) are schematic views for illustrating a method offorming a pattern including a single buffer layer by use of thenear-field exposure photomask in Embodiment 1 of the present invention.

FIG. 6 is a schematic view showing a structure of a near-field opticalhead in Embodiment 2 of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention is characterized in that a near-field lightgenerating method, a higher intensity near-field light is obtained byusing a rectangular opening having a length (long side) and a width(short side) which are different from each other (herein simply referredto as “rectangular opening”).

Hereinbelow, the present invention will be described with reference tothe drawings.

FIG. 1 shows a structure of a near-field exposure mask (photomask)according to an embodiment of the present invention.

In FIG. 1, the near-field exposure mask includes a mask base material101 which is transparent to light source wavelength, a metal film 102having a thickness t disposed thereon, a substrate 103 for supportingthe mask base material 101, a rectangular fine opening pattern 104,disposed in the metal film 102, having a size of not more than thewavelength, and a slit-like fine opening having a width of not more thanthe wavelength. The mask base material comprises a 0.1-100 μm thick filmand is supported on the substrate 103.

The photomask is, as described later, caused to closely contact a thinfilm resist applied onto a substrate and is irradiated with light fromthe mask base material side to be used for pattern exposure.

Hereinbelow, a distribution of near-field light by the rectangular fineopening provided in the photomask described above will be explained onthe basis of an analysis result according to finite difference timedomain method.

In the analysis, calculation is performed on the precondition that amask comprising SiN layer and a 50 nm-thick Cr film disposed thereon isplaced in such a state that it closely contacts a sufficiently thickphotoresist. A wavelength of light from a light source is 436 nm (g lineas an emission line of Hg) in a vacuum. The calculation results areshown with respect to two polarization directions perpendicular to eachother and are obtained, respectively, by adding an independentlycalculated result of light intensity. The mask used comprises a lightblocking film of Cr provided with a fine opening.

FIG. 2(a) shows a near-field distribution in the neighborhood of therectangular opening having a size of 40 nm (width)×60 nm (length).

In FIG. 2(a), a solid line represents an iso-intensity line of anintensity of 0.3 in the case where an intensity of incident light istaken as 1. As shown in FIG. 2(a), at a depth of 20 nm in the resist, itis found that the near-field distribution has an exposure of 50 nm in xdirection and 40 nm in y direction. Further, a dashed line represents aniso-intensity line of an intensity of 0.3 in a near-field distributionat a cross section of a 40 nm-wide slit-like opening (long slit) whichis disposed together with the fine opening.

FIG. 2(b) shows, as a comparative embodiment, a near-field distributionin the neighborhood of a square opening having a size of 40 nm×40 nm.

The near-field in the neighborhood of the square opening has anintensity lower than that in the neighborhood of the rectangularopening. Accordingly, in this embodiment, a solid line represents aniso-intensity line of an intensity of 0.15 in the case of the incidentlight intensity of 1. The iso-intensity line shows that the intensity ofthe incident light is such an extent that the incident light reaches adepth of 25 nm. It is found that the resultant spot has a size of 50nm×50 nm at a depth of 20 nm. Further, a dashed line represents aniso-intensity line of an intensity of 0.15 in a hear-field distributionat a cross section of a 40 nm-wide slit-like opening (long slit)disposed together with the fine opening and a shows a profile whichextends in a direction along the mask surface.

From the above results of calculation, the following points have beenfound.

One is that a distribution intensity of near-field light in theneighborhood of the rectangular fine opening is higher than that of thesquare fine opening.

In the case where an exposure condition is selected on the basis offormation of a latent image, having a desired size, which reaches adepth of 20 nm of the resist and the rectangular opening is used withrespect to the resist, it is found that an exposure time may bedetermined so that the iso-intensity line of an intensity of 0.3provides a limit of solubility/insolubility of the resist. Further, byeffecting the exposure for such an exposure time, a 80 nm-wide linepattern can be formed in a depth of 20 nm even when the slit-like fineopening is used. In order to provide a line pattern having a widthsubstantially equal to that of a spot, the width of the slit-like fineopening may be further narrowed. More specifically, when a slit-likeopening is formed with a width of 30 nm, a line pattern with a width of50 nm can be formed in a depth of 20 nm in the resist.

On the other hand, in the case where the photomask having a squareopening is used, the distribution intensity of near-field light is low.For this reason, in order to form the latent image which reaches thedepth of 20 nm similarly as in the above described case, it is necessaryto effect exposure for such a time that the iso-intensity line of anintensity of 0.15 provides a limit of solubility/insolubility of theresist. In other words, it is necessary to take an exposure timesubstantially two times that in the case of the rectangular opening.Further, when the same exposure condition is applied to the slit-likepattern, the resultant line pattern is subjected to excessive exposure.As a result, it is difficult to form a desired line pattern (FIG. 2(b)).

In this embodiment, the above described results are based on oncecalculation example but a similar tendency is shown with respect to anopening having a size of not more than the wavelength of light. When therectangular opening having a length and a width which are different fromeach other is used, it becomes possible to obtain near-field lighthaving a higher intensity than the case of using the square opening.This is because as one of a length and a width of the square opening isgradually increased to change the length and the width of the squareopening, an intensity of near-field light leaking from the resultantopening becomes abruptly higher. More specifically, a degree ofattribution of a vector component parallel to the short side (width) ofelectric field vectors directed in two polarization directions isprincipally increased. However, light of such a polarization componentis directed so that an electric field in the neighborhood of the shortside of the rectangular opening is parallel to an interface. As aresult, an intensity of near-field immediately in the neighborhood ofthe short side does not become higher. That is when the shape of theopening is changed from a square to a rectangular, the opening isparticularly irradiated with a polarized component of light an electricfield vector of which is parallel to the short side of the opening,thereby to immediately increase an intensity of light leaking from theopening. On the other hand, a degree of expansion of near-field light bysuch a polarized component is moderate, so that, it becomes possible toobtain a higher-intensity near-field light when the rectangular openinghaving a length and a width which are different from each other.

In the case where the above described phenomenon is used for near-fieldexposure, it is possible to set such an exposure condition that ahigher-intensity iso-intensity line provides the limit ofsolubility/insolubility of the resist. For example, in the case ofassuming a certain exposure condition which permits formation of alatent image having a desired size in a desired depth of the resist,with respect to a standard square opening, one of adjacent sides of theopening is increased to provide a rectangular opening. As a result, theintensity of near-field light can be increased. In this case, it is notnecessary to effect polarization control of light with respect to thelight source. When the intensity of near-field light becomes higher, itis possible to provide an equivalent amount of exposure light byeffecting exposure in a shorter time. As an iso-intensity line (e.g., anintensity I0) being a measure of latent image formation, a newiso-intensity line having a higher intensity (e.g., an intensity I1(e.g., I1=2×I0) compared with the case of the square opening is used.The iso-intensity line of intensity I0 becomes broader with an increasein long side of the rectangular opening but the new iso-intensity lineof intensity I1 may be used for exposure. As a result, it becomespossible to effect exposure in a short time without causing a remarkableincrease in latent image size.

In view of the calculation results, a ratio of length of width(length/width ratio) of the rectangular opening for use with exposure inaccordance with the above described mechanism may appropriately be about1.5. Further, in order to significantly enhance the light intensitycompared with the case of square opening, the length/width ratio isrequired to be at least 1.1 times that of the square 0.

On the other hand, in order to provide a length/width ratiosubstantially equal to that of the square opening (e.g., not more than1.1 times that (=1) of the square opening) when a fine light spot isformed by use of the rectangular opening in the neighborhood of the fineopening at an opening portion on the light incident side, it isnecessary to provide the fine opening with the length/width ratio whichis two times that of the square opening. In other words, in the presentinvention, the fine opening may preferably have a length/width ratio of1.1-2. As described above, when the rectangular opening is used withreference to the results of analysis of electromagnetic field, it ispossible to obtain a light intensity which is not less than 2 times thatof the square opening. As a result, it is found that it becomes possibleto reduce the exposure time required for forming the latent image whichreaches the same depth in the resist. Further, as shown in FIG. 1, whenthe photomask has the rectangular opening and the slit-like opening incombination, it is found that both patterns of the rectangular openingand the slit-like opening can be used for patterning under the sameexposure condition.

Hereinbelow, embodiments of the present invention will be described morespecifically.

EMBODIMENT 1

FIG. 3 shows a structure of a near-field exposure apparatus inEmbodiment 1 of the present invention.

In the near-field exposure apparatus, a near-field exposure mask 301provided with a fine opening pattern in combination with a slit-likeline pattern which has a length larger than a wavelength of light. The Anear-field exposure mask 301 has the patterns in a light blocking filmformed on an elastic mask base material. Herein, a “front surface” ofthe mask refers to a surface where the light blocking film (for themask) is disposed, and a “rear surface” refers to a surface oppositefrom the front surface.

In this embodiment, the front surface of the photomask 301 is disposedapart from a pressure adjusting (regulating) vessel 305 and the rearsurface is disposed to face the pressure adjusting vessel 305. Thepressure adjusting vessel 305 is designed to permit adjustment ofpressure therein by a pressure adjusting means 313.

A member to be exposed comprises a substrate 306 and a resist film 307disposed on the surface of the substrate 306 (hereinafter referred to asthe “resist 307/substrate 306”).

The resist 307/substrate 306 is mounted on a stage 308 and the stage isdriven to effect relative positional alignment of the substrate 306 withthe photomask 301 in a two-dimensional direction with respect to themask surface.

Next, the stage 308 is moved in a direction of a normal to the masksurface to bring the photomask 301 into close contact with the resist307 disposed on the substrate 306.

During the close contact operation, the pressure in the pressureadjusting vessel 305 is adjusted by the pressure adjusting means 313 sothat a distance between the entire front surface of the photomask 301for evanescent light and the resist 307 disposed on the substrate 306becomes not more than 100 nm. Thereafter, exposure light emitted from anexposure light source 309 is changed to parallel light by a collimatorlens 311 and passed through a glass window 312 to be introduced into thepressure adjusting vessel 305. The evanescent light exposure mask(photomask) 301 is irradiated with the light from its rear surface side.At that time, exposure of the resist 307 is performed by near-fieldlight generated adjacent to the fine opening at the front surface of thephotomask 301.

The mask pattern includes, as shown in FIG. 1, independent rectangularopenings and a slit-like line pattern, having a length larger than thewavelength of light, in combination with the independent rectangularopenings. Each of the rectangular openings has a width (short side) of40 nm and a length (long side) of 60 nm, and the slit-like line patternhas a width of 30 nm.

A method of manufacturing the A near-field exposure mask in thisembodiment will be described in detail with reference to FIG. 4.

As shown in FIG. 4(a), on a 500 μm-thick double-sided polished substrate401 of Si (Si (100) substrate 401), a 0.8 μm-thick SiN film 402 as amask base material is formed at the front surface (an upper surface inFIG. 4(a)) of the substrate 401 by LP-CVD (low pressure-chemical vapordeposition) method, and a 0.8 μm-thick SiN film 403 as an etching windowis formed at the rear surface (a lower surface in FIG. 4(a)) by LP-CVDmethod. Thereafter, on the surface of the SiN film 402, a 70 μm-thick Crfilm 404 is formed by vapor deposition method while effecting control offilm thickness by a film thickness monitor by use of quartz oscillator.

Then, onto the surface of the Cr film 404, a resist 405 for electronbeam is applied, and a pattern 407 including a width of 20 nm and awidth of 50 nm is formed by electron beam 406 (FIG. 4 (b)). Afterdevelopment, After development, the resist 405 is subjected to dryetching with CCl₄ to provide a fine opening pattern 408 (FIG. 4(c)).

A part of the SiN film 403 (formed at rear (lower) surface of thesubstrate 401) is removed to form a window 409 for etching (FIG. 4(c)).Anisotropic etching with KOH solution is performed from the rear (lower)surface side of the substrate 401 to remove a part of the Si substrate401 to provide a mask 410 principally comprising the SiN film 402 andthe Cr film 404 (FIG. 4(d)).

In this embodiment, in the step of forming the fine opening pattern 408in the Cr film 404, the electron beam processing is employed but otherprocessing methods, such as focused ion beam processing, X-raylithography, and scanning probe microscope (SPM) processing, may beused. Of these processing methods, such a processing that the SPMtechnique represented by scanning tunnel microscope (STM), atomic forcemicroscope (AFM) or scanning near-field optical microscope (SNOM) isapplied thereto, may preferably be used since it becomes possible toform a very fine opening pattern of not more than 10 nm when formationof the fine opening pattern is performed by the processing.

Referring gain to FIG. 3, as a material for the resist 307, aphotoresist material used in an ordinary semiconductor process may beselected.

With respect to the resist material, a wavelength of light which permitsexposure is in the range of about 200-500 nm. However, when aphotoresist which is sensitive to g line and i line of mercury (Hg) lampin a wavelength range of 350-450 nm is selected, it becomes to allowmore process latitude and reduction in cost since such a resist materialhas a great choice and is relatively inexpensive.

The exposure light source 309 is required to emit light having anexposable wavelength with respect to the resist 307 used. For example,when the photoresist for the above described g line or i line (of Hg) isselected as the resist 307, as the light source 309, those includingHeCd laser (light wavelength: 325 nm, 442 nm), GaN-type bluesemiconductor laser (410 nm), second or third harmonic generation (SHGor THG) laser of infrared light laser, and a mercury (Hg) lamp (g line:436 nm, i line: 365 nm) may be used.

An amount of exposure light is adjusted by controlling a drive voltage,a drive current and irradiation time of the exposure light source 309.In this embodiment, the g line (wavelength: 436 nm) of the Hg lamp isused, so that an area of 100 nm×100 nm is irradiated with the g linelight by use of a collimator lens through a wavelength selection filter.A power of the light is monitored by a power meter, and an exposure timeis set so that the light exposure amount of the resist exceeds athreshold with respect to exposure. In this case, it is necessary toadjust the light exposure amount in view of light transmittance of thephotomask as the exposure is performed through the photomask.

FIGS. 5(a) to 5(d) are views for illustrating a method of forming apattern including one buffer layer by use of the A near-field exposuremask in this embodiment.

FIG. 5(a) shows a photomask 504 and a member to be exposed to light.

The photomask 504 is a photomask identical to that described above withreference to FIG. 3.

Onto an Si substrate 501, a positive photoresist is applied by use of aspin coater and heated at 120° C. for 30 minutes to form a 400 nm-thickfirst layer 502. Onto the first layer 502, an Si-containing negativephotoresist is applied and pre-baked to form a 20 nm-thick second layer503.

The Si substrate 501 onto which the photoresist having a two-layerstructure is applied and the photomask 504 are caused to come close toeach other by the near-field exposure apparatus, and pressure is appliedthereto to bring the resist layer 503 and the photomask 504 in closecontact with each other.

The resultant structure is irradiated with exposure light 505 throughthe photomask 504, whereby the pattern on the photomask 504 is exposedto the light and thus a portion 506 of the photoresist layer 503 is alsoexposed to light (FIG. 5(b)). Thereafter, the photomask 504 is removedfrom the photoresist surface, and the photoresist 503 is subjected todevelopment and post baking, whereby the pattern on the photomask 504 istransferred to the photoresist as a resist pattern (FIG. 5(c)).

Thereafter, by using the pattern of the photoresist (second layer) 503as an etching mask, the photoresist (first layer) 502 is etched byoxygen reactive ion etching (FIG. 5(d)). The oxygen reactive ion etchinghas a function of oxidizing Si contained in the photoresist (secondlayer) 503 to increase a resistance to etching of the second layer.

As described above, it becomes possible to transfer various patterns onthe photomask onto the substrate 501 as a resist pattern with a clear(high) contrast.

EMBODIMENT 2

FIG. 6 shows a structure of an optical head in Embodiment 2 of thepresent invention.

In FIG. 6, a slider 602 is held by an unshown arm so that it is apartfrom an optical disk 601, such as a magento-optical disk or an opticaldisk using fine pits or phase change recording, by a predetermineddistance. The predetermined distance is substantially not more than asize of an opening of a near-field light source. The slider 602 isreciprocated by an unshown actuator in a predetermined range on theoptical disk 601. On the slider 602, a near-field probe 603 according tothe present invention as a near-field light source is mounted. Thenear-field probe 603 is irradiated, though an objective lens, with lightfrom a semiconductor laser light source which is not mounted on theslider 602 after being shaped into a collimated beam by a collimatorlens. A focus of the objective lens is controlled by a drive actuator soas to follow with respect to (external) disturbance such as a verticalmotion of the optical head depending on an unevenness of the medium.

The near-field probe 603 in the present invention comprises a glasssubstrate and a thin metal film 604, provided with a rectangular fineopening 605, disposed on the glass substrate. The rectangular fineopening 605 has an opening size of 80 nm (width)×120 nm (length).Compared with a square fine opening having an opening size of 80 nm×80nm, the rectangular fine opening provides a light intensity which is 1.5times that of the square fine opening without substantially increasing asize of a resultant near-field light spot. Accordingly, it is possibleto provide an efficient optical head.

A change in reflection characteristic of the optical disk 601 leads to achange in scattering characteristic of near-field light, so that itbecomes possible to read information recorded in the disk as a change inamount of light returned to the optical head through the fine opening.

Further, by disposing a magnetic recording head in the neighborhood ofthe optical head and locally heating a recording medium throughnear-field light energy, it is also possible to provide a light-assistedmagnetic recording head which facilitates magnetic writing.

The optical head, as a light source, for effecting recording in theoptical disk can also be utilized as an illumination-mode near-fieldoptical microscope. The optical head, as a light source, for readinginformation from the optical disk can also be utilized as anillumination/light-gathering mode near-field optical microscope. Inthese cases, a near-field optical microscope apparatus is constituted bya sample stage for permitting two-dimensional scanning of a sample bymounting the sample thereon and a probe-driving system for bringing anear-field light source near to the sample. More specifically, theprobe-driving system includes a cantilever, a piezoelectric actuator,etc., and controls a distance between the near-field light source andthe sample.

INDUSTRIAL APPLICABILITY

As described hereinabove, according to the present invention, it ispossible to provide a method of generating near-field light, capable ofgenerating a higher-intensity near-field light at a high efficiency.Further, it is also possible to provide a near-field exposure mask, anear-field exposure

method, a near-field exposure apparatus, and a near-field optical head,which are usable in the near-field light generating method incombination. It is further possible to provide a near-field opticalmicroscope and a recording and reproducing apparatus which employ thenear-field optical head.

1. A near-field light generating method for forming a fine light spot ata portion adjacent to a fine opening having a size of not more than awavelength of light on a light outgoing side of the fine opening byirradiating the fine opening with the light, said method comprising:forming a light spot having a length and a width which are substantiallyequal to each other by the fine opening, the fine opening having arectangular shape having a length and a width which are different fromeach other.
 2. A method according to claim 1, wherein the length and thewidth of the light spot are determined by the width of the rectangularopening.
 3. A method according to claim 1, wherein the fine opening hasa length/width ratio of 1.1-2.
 4. A method according to claim 1, whereinthe fine opening is provided in a plurality of fine openings includingthe rectangular opening and a slit-like opening.
 5. A near-fieldexposure mask, comprising: a mask base material, a light blocking layerdisposed on the mask base material, and a fine opening having a size ofnot more than a wavelength of light used for exposure, wherein the fineopening comprises a rectangular opening having a length and a widthwhich are different from each other, the rectangular opening having alength/width ratio which permits transfer of a pattern having a lengthand a width which are substantially equal to each other.
 6. A maskaccording to claim 5, wherein the fine opening has a length/width ratioof 1.1-2.
 7. A mask according to claim 5, wherein the fine opening isprovided in a plurality of fine openings including the rectangularopening and a slit-like opening.
 8. A near-field exposure method,comprising: providing a near-field exposure mask according to claim 5,and exposure an exposure object to light by using the near-fieldexposure mask.
 9. A near-field exposure apparatus for exposing anexposure object to light, comprising: a near-field exposure maskaccording to claim 5, and a light source to be exposed to light.
 10. Anear-field optical head, comprising: means for generating near-fieldlight, provided with a rectangular fine opening having a size of notmore than a wavelength of light or a combination of the rectangular fineopening and a slit-like opening, wherein a light spot having a lengthand a width which are substantially equal to each other by therectangular fine opening, is formed at a portion adjacent to an openingportion on a light outgoing side of the rectangular fine opening.
 11. Ahead according to claim 10, wherein the fine opening has a length/widthratio of 1.1-2.
 12. A near-field optical microscope for effectingsurface observation of a sample, comprising: a near-field optical headaccording to claim
 10. 13. A recording and reproducing apparatus foreffecting recording and reproduction with respect to a recording medium,comprising: a near-field optical head according to claim 10.